1. Field of the Invention
This invention relates to fire prevention and the electrical power industry, namely, to methods and devices for detecting fire originating from faults in electric networks (EN) or electric installations (EI) in buildings, constructions, houses, aircrafts, vessels, railway services and other installations.
2. Discussion of Related Art
Fire or explosions occasionally occur in dwellings, households, industrial and other installations, and originate from faults in electric networks and electric installations. Besides the basic faults, often accompanied by financial damage, death and/or permanent injury of people, sparking occurs in wiring, short circuit, and fold back current, creeping current, and large inadmissible reduction in line voltage. In Russia, according to official statistics, the impact of electrical installation fire is the second biggest problem after careless fire handling. The above specified faults are especially hazardous in the exploitation of advanced hazard facilities in the following industry branches: oil and gas production, storage and shipment, mineral industry, poisonous and explosive materials, and many other special, military and civil designation facilities with fire and explosion hazard.
For detection of these faults a number of methods and protection devices, used in EN and EI, have been developed. Among them a well-known device called Emergency Circuit Breaker (ECB), as shown in FIG. 4.7 of Reference [1] contains a differential current measurement sensor (ZFSCT—zero-phase sequence current transformer), an electromagnetic signal generator of power network shutdown, and an actuating device (release device), shutting down EN and EI in case the tracked resistance surpasses admissible values, thus preventing an electric shock or a fire.
A short-circuit protection device is shown in FIG. 4.8 of Reference [1] and contains a sensor-turn located on the release device and connected in series into the current circuit burden, shutdown signal generator (release device) and actuating device, disabling EN or EI in case the intensity of current achieves intensity of short circuit.
This device can be used for falling voltage protection if it has a winding minimum-current release device.
A protection device against overload current is shown in FIG. 4.30 of Reference [1] and contains a bimetallic release device interacting with a cogged release arm, a shaped piece, a spring with levers and contact points of the circuit-breaker.
A method and device for fire prevention of sparking in the electric network or electric installation and its realization is taught by Reference [2]. It has a wide collection of general properties, applicable to technical devices mentioned above, and is among the known and accepted prior art.
According to the well-known engineering solutions, the current of the controlled section of EN or EI is measured. The signal of the second and/or higher harmonic is singled out of the measured current by filtration of actual frequency or the low-frequency spectrum. The second harmonic characterizes the reduction process of voltage across the broken circuit with the current flow sparking through zero value. The value of the extracted signal is defined by the intensity and value of this sparking current, which depends on transient resistance. Then, the signal is strengthened and straightened. Meanwhile, the signal accumulation is performed with the previously estimated amount of the sparking current. The value of the sparking current is calculated on a measurement basis and subsequent calculation of each selected option of a cycle “arc striking-extinction”, forming and fading stages, in the segments of the sparking current transition through null. To the cycle index, depending on the sparking current value, we apply, for example, repetition of the rate of the cycle, the duration of the forming and fading stages of the cycle, the quantity of pulses on the fading stage of the cycle with amplitude exceeding the specified value. The signal accumulation results, for the present time, are balanced against the preset admissible values. Meanwhile, the output of the device forms the clearance signal notifying of corresponding level of fire hazard and/or the shutdown command for the controlled section of inoperative EN or EI, which proceeds to the information display package and/or to the shutdown module of the controlled section of EN or EI.
The device of Reference [2] for realization of the specified method contains an evaluator of the sparking current value, which includes a module of signal-symptom generation of the cycle “arc striking-extinction”, which provides the formation of the second or higher harmonic component signal pulse, a symptom cycle for the very cycle “arc striking-extinction”; a module of cycle index measurement and calculation or providing the formation on the first signal pulse, symptom of the time frame cycle, during which the signals of pulse-symptom are accumulated, and on completion of which recurrence rate of these cycles are estimated; and/or providing determination of duration of the formation and fading stages of the cycle and/or providing determination of quantity of pulses of the fading stage of the cycle with amplitude exceeding the specified values; a module of sparking current value calculation based upon or calculated upon the recurrence rate cycle and/or based upon the duration of the forming and fading stages of the cycle, and/or based upon the quantity of pulses of the fading stage of the cycle with amplitude exceeding the specified values; a storage module for the estimated sparking current value, providing memorization of the estimated sparking current value and its transferring to the accumulation module. The accumulation module is made with the possibility of reception of the estimated sparking current value, receiving commands from the control module on formation of the definite time interval, and realization within this time range signal accumulation by addition, upon entry of the very signal pulse, of symptom cycle of “arc striking-extinction”, to preceding stack number corresponding to the estimated sparking current value. The control module is accomplished with the possibility of signal reception for realization of the specified command production with transferring of the estimated sparking current value to the accumulation module. All the commands on execution of the preset operation algorithms of the device are formed in the control module, performed, for example, in the form of a microcontroller. The power supply of the device has a supply unit, which is in turn supplied by EN and of a field ion source.
The disadvantages of the provided engineering solution includes the absence of magnitude of pulse value direct determination on forming and fading stages of the cycle “arc striking-extinction” and/or the measurement on the forming stage of a cycle, the quantity of pulses with amplitude exceeding the specified value, which could ensure the most positive and adequate definition of the sparking current strength under the severe service conditions provided to the device.
Besides, an essential complexity of the object support process by a complex protection adds an independence of the above mentioned devices on circuit from each other and design, replication of the same functions, implemented in many instances by common modules and circuit design.
Therefore, the separate application of all the essential protection devices into a fire and explosion prevention system not only practically complicates and increases the price of their usage, but generally also reduces the reliability of the electric system.